The disclosure of Japanese Patent Application No. 2002-171247 filed on Jun. 12, 2002, including its specification, drawings and abstract, is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to a technology for calculating a deterioration degree of a battery which deteriorates while being used. More particularly, the invention relates to a deterioration degree calculating apparatus and a deterioration degree calculating method for a secondary battery mounted in a vehicle.
2. Description of the Related Art
Recently, a vehicle has been developed, which is provided with a power train using two types of power sources, that is, a gasoline engine that is an internal combustion engine and an electric motor. Such a power train is referred to as a hybrid system. The electric motor is driven by electric power supplied from a battery mounted in the vehicle. For example, when an alternating current motor is used as the electric motor, direct current electric power output from the battery is converted to alternating current electric power by a circuit such as an inverter, and the electric motor is driven by the alternating current electric power.
The battery used in such a hybrid system needs to be reliable because it relates to running of the vehicle. The deterioration degree of the battery depends on the state of use, as well as elapsed years after the start of use. Therefore, it is difficult to determine the deterioration degree of the battery based only on elapsed years after the start of use.
Japanese Patent Laid-Open Publication No. 52-145734 discloses a method of determining a lifetime of such a secondary battery. The method of determining a lifetime of a secondary battery disclosed in the patent publication includes the steps of measuring elapsed years after the start of use, external appearance, variations in cell voltage at the time of floating charge or equalizing charge, charging current, variations in specific gravity of electrolyte, electrostatic capacity at the time of floating charge, and internal resistance which are factors closely correlated with aged deterioration of the secondary battery; ranking the results of the determination; and determining a lifetime and a residual lifetime of the battery based on the total score obtained by summing each score set for each rank of each factor.
According to the method of determining a lifetime of a battery disclosed in the aforementioned patent publication, quantity states of various factors concerning the secondary battery are measured. With regard to each of factors closely correlated with the deterioration of the battery, the degree of the influence on the deterioration state of the secondary battery is classified as, for example, one of four ranks based on the range of a measured value. A score is set for each rank, and the rank is calculated based on the measured value. The lifetime of the secondary battery is determined based on the total score obtained by summing each score set for each rank of each factor.
In the method of determining a lifetime of a battery disclosed in the aforementioned patent publication, for example, a skilled person performs ranking and sets a score corresponding to each rank for calculating the total score, based on the skilled person""s experience. As disclosed in the aforementioned patent publication, there are various factors concerning the lifetime of the secondary battery, and the lifetime of the secondary battery is determined using the fixed ranks and scores for the various factors. Therefore, the lifetime of the secondary battery cannot be accurately determined.
It is an object of the invention to provide a deterioration degree calculating apparatus and a deterioration degree calculating method for a battery which can accurately determine a lifetime of a battery and can generate information based on the lifetime.
A deterioration degree calculating apparatus according to a first aspect of the invention includes a detector that detects plural state quantities of a battery; a processor that calculates plural deterioration degrees based on the detected plural state quantities; a storing device that stores contribution degrees each of which corresponds to each of the deterioration degrees; the processor calculating a total deterioration degree based on the deterioration degrees and the contribution degrees; and the processor calculating the contribution degrees.
According to the first aspect of the invention, the detector detects, for example, a temperature of a secondary battery, a charging/discharging current value of the battery, a quantity of change in a state of charge (SOC) of the battery. The processor calculates, for example, a deterioration degree of the battery based on the temperature of the battery, a deterioration degree of the battery based on the charging/discharging current value of the battery, and a deterioration degree of the battery based on the quantity of change in the SOC of the battery. The processor calculates the total deterioration degree by multiplying each of the deterioration degrees by the corresponding contribution degree, and summing the values obtained by multiplication. The processor changes one or more of the contribution degrees to be used when the deterioration degrees are multiplied next time (for example, increases a contribution degree corresponding to a specific deterioration degree), for example, when the calculated total deterioration degree is large (when deterioration has progressed). Thus, it is possible to calculate the total deterioration degree which more accurately corresponds to the residual lifetime of the secondary battery. As a result, it is possible to provide the deterioration degree calculating apparatus for a battery which can accurately determine the lifetime of the secondary battery.
In the first aspect of the invention, the processor may calculate plural deterioration degrees based on the temperature of the battery, the charging/discharging current value, and the SOC of the battery. Thus, the deterioration degree can be accurately calculated based on the temperature of the battery, the charging/discharging current value of the battery, and the SOC of the battery that have large influences on the deterioration of the secondary battery, for example, by integrating the state quantities thereof with respect to time.
In the first aspect of the invention, the deterioration degree calculating apparatus may further include a generating device which generates, based on the calculated total deterioration degree, information concerning a limit on the use of the battery. Thus, in the case where the battery is mounted in a vehicle and the battery is used as a secondary battery for driving the vehicle, when the secondary battery severely deteriorates and the calculated total deterioration degree indicates that the end of the lifetime of the secondary battery has been reached, information for suppressing further deterioration is generated in order to prevent the vehicle from becoming unable to run using the secondary battery. For example, this information is used for limiting electric power input to the secondary battery and electric power output from the secondary battery, or limiting the usable range of the SOC of the battery to a small range. Thus, it is possible to avoid a situation where the secondary battery becomes unable to completely function and the vehicle stops before replacement of the secondary battery is performed.
In the first aspect of the invention, the deterioration degree calculating apparatus may further include a generating device which generates, based on the calculated total deterioration degree, information concerning a warranty on the battery. Thus, it is possible to set the warranty period to a period until the end of the lifetime of the secondary battery that is actually determined based on the total deterioration degree, while the warranty period is usually set based on elapsed time after the start of use or the like.
In the first aspect of the invention, the deterioration degree calculating apparatus may further include a remaining value generating device which generates, based on the calculated total deterioration degree, information concerning a remaining value of the battery. Thus, it is possible to determine the remaining value of the battery based on the total deterioration degree which indicates an actual deterioration degree, while the remaining value of the battery is usually determined based on elapsed time after the start of use, or the like.
In the first aspect of the invention, the battery may be a battery for driving a vehicle, which is mounted in the vehicle. Thus, it is possible to accurately calculate the actual lifetime of the battery for driving the vehicle based on the total deterioration degree thereof, and to perform replacement of the battery before the vehicle may become unable to run.
In the first aspect of the invention, the deterioration degree calculating apparatus may further include a remaining value generating device which generates, based on the calculated total deterioration degree, information concerning a remaining value of the vehicle.
In the first aspect of the invention, it is possible to determine the remaining value of the vehicle using the battery as a driving source based on the total deterioration degree which indicates the actual deterioration degree, while the remaining value of the vehicle is usually determined based on a running distance or elapsed years after the vehicle starts to run.
In the first aspect of the invention, the deterioration degree calculating apparatus may further include a deterioration degree storing device that stores the total deterioration degree. Furthermore, the deterioration degree storing device may hold the total deterioration degree even when power supply is interrupted.
A deterioration degree calculating method for a battery according to a second aspect of the invention includes a detecting step of detecting plural state quantities of a battery; a first calculating step of calculating plural deterioration degrees based on the detected plural state quantities; a storing step of storing contribution degrees each of which corresponds to each of the plural deterioration degrees; a second calculating step of calculating a total deterioration degree of the battery based on the deterioration degrees and the contribution degrees; and a third calculating step of calculating the contribution degrees based on the calculated total deterioration degree.
According to the second aspect of the invention, in the detecting step, for example, a temperature of the secondary battery, a charging/discharging current value of the battery, and a quantity of change in a state of charge (SOC) of the battery are detected. In the first calculating step, for example, a deterioration degree of the battery based on the temperature of the battery, a deterioration degree of the battery based on the charging/discharging value of the battery, and a deterioration degree of the battery based on the quantity of change in the SOC of the battery are calculated. In the second calculating step, the total deterioration degree of the battery is calculated by multiplying each of the deterioration degrees by the corresponding contribution degree stored in the storing step, and summing the values obtained by multiplication. In the third calculating step, one or more of the contribution degrees to be used when the deterioration degrees are multiplied next time are changed (for example, a contribution degree corresponding to a specific deterioration degree is increased), for example, when the calculated total deterioration degree is large (when deterioration has progressed). Thus, it is possible to calculate the total deterioration degree which more accurately corresponds to the residual lifetime of the secondary battery. As a result, it is possible to provide a deterioration degree calculating method for a battery which can accurately determine the lifetime of the secondary battery.
In the second aspect of the invention, the first calculating step may calculate plural deterioration degrees based on the temperature of the battery, the charging/discharging value of the battery, and the SOC of the battery. Thus, the deterioration degree can be accurately calculated based on the temperature of the battery, the charging/discharging current value of the battery, and the SOC of the battery that have large influences on the deterioration of the secondary battery, for example, by integrating the state quantities thereof with respect to time.
In the second aspect of the invention, the deterioration degree calculating method may further include a generating step of generating, based on the calculated total deterioration degree, information concerning a limit on the use of the battery. Thus, in the case where the battery is mounted in a vehicle, and the battery is used as a secondary battery for driving the vehicle, when the secondary battery severely deteriorates and the calculated total deterioration degree indicates that the end of the lifetime of the secondary battery has been reached, information for suppressing further deterioration is generated in order to prevent the vehicle from becoming unable to run using the secondary battery. For example, this information is used for limiting electric power input to and output from the secondary battery, or limiting the usable range of the SOC of the battery to a small range. Thus, it is possible to avoid a situation where the secondary battery becomes unable to completely function and the vehicle stops before replacement of the secondary battery is performed.
In the second aspect of the invention, the deterioration degree calculating method may include a generation step of generating, based on the calculated total deterioration degree, information concerning a warranty of the battery. Thus, it is possible to set the warranty period to a period until the end of the lifetime of the secondary battery that is actually determined based on the total deterioration degree, while the warranty period is usually set based on elapsed time after the start of use or the like.
In the second aspect of the invention, the deterioration degree calculating method may further include a remaining value generating step of generating, based on the calculated total deterioration degree, information concerning a remaining value of the battery. Thus, it is possible to determine the remaining value of the battery based on the total deterioration degree which indicates an actual deterioration degree, while the remaining value of the battery is usually determined based on elapsed time after the start of use, or the like.
In the second aspect of the invention, the battery may be a battery for driving a vehicle, which is mounted in the vehicle. Thus, it is possible to accurately calculate the actual lifetime of the battery for driving the vehicle based on the total deterioration degree thereof, and to perform replacement of the battery before the vehicle may become unable to run.
In the second aspect of the invention, the deterioration degree calculating method may further include a remaining value generating step of generating, based on the calculated total deterioration degree, information concerning a remaining value of the vehicle. Thus, it is possible to determine the remaining value of the vehicle using the battery as a driving source, based on the total deterioration degree which indicates the actual deterioration degree, while the remaining value of the vehicle is usually determined based on a running distance or elapsed years after the vehicle starts to run.
In the second aspect of the invention, the deterioration degree calculating method may further include a deterioration degree storing step of storing the total deterioration degree. Furthermore, the total deterioration degree may be held even when power supply is interrupted.
A deterioration degree calculating apparatus according to a third aspect of the invention includes detecting means for detecting plural state quantities of a battery; processing means for calculating plural deterioration degrees based on the detected plural state quantities; storing means for storing contribution degrees each of which corresponds to each of the deterioration degrees; the processing means calculating a total deterioration degree based on the deterioration degrees and the contribution degrees; and the processing means calculating the contribution degrees.